Around 1% of the US population experience inflammatory diseases of the intestine. Prolonged inflammation and tissue injury has also been proposed to potentiate gastrointestinal (GI) cancer. To understand how cells in the GI tract interact with wide varieties of microbes and pathogenic substances is important for developing therapeutic strategies that alleviate intestinal diseases. This proposal focuses on understanding how Drosophila intestinal stem cells (ISCs) mediate repair after tissue damage. Drosophila midgut has a relatively simple cellular organization, and midgut ISCs have recently been identified that function to replenish the different cell types. Our preliminary results demonstrate that Drosophila ISCs can increase their division rate in response to tissue damage. Using this newly established system, the genetic requirement of insulin receptor is clearly shown to be essential for ISC division. A number of new genes that can regulate ISC growth and division have also been identified via a pilot genetic screen. Because this Drosophila ISC system is relative new and so far very few genes are known to be involved, it is important to first identify more essential genes by genetic approach and establish the framework that regulates ISC division. A well-established genetic framework will help to understand the molecular mechanisms by which ISCs respond to environmental challenges and mediate tissue repair. This proposal includes three specific aims: 1. Test whether insulin signaling is instructive or permissive in ISC division; 2. Investigate how Tuberous Sclerosis Complex interacts with the insulin pathway in ISC growth; 3. Identify and analyze new components in damage-induced ISC division. The results obtained from studying the genetically amenable Drosophila ISCs should provide important insights into human stem cell- mediated tissue repair, intestinal inflammatory diseases and cancer progression.